Apparatus for determining the tensile stress in a continuously moving web of material

ABSTRACT

An apparatus for measuring the tensile stress of a continuously moving gas and liquid impermeable web of material, including a pair of spaced apart rollers disposed below the web for deflecting the web of material; an elongated enclosed channel disposed between the rollers below the web having an axial length which is at least as great as the width of the web and an opening disposed therebeneath; a plurality of orifices disposed in the channel coupled to means for supplying a gas under constant pressure thereto for forming a static pressure cushion between the web and the channel; and measuring means disposed in the channel for measuring the pressure therein. The improvement of the invention comprises a plurality of triangular shaped chambers which are axially disposed in series in the channel. Each of the chambers includes a partition member disposed parallel to the direction of movement of the web which forms at least one wall of each of the triangular shaped chambers. Selected ones of the chambers disposed at the outermost axial ends of the channel are provided with additional orifices communicative with the channel and coupled to means for controlling the supply of gas thereto from the channel, for compensating for gas losses at the lateral edges of the web.

Elite States Patent [1 1 Breyer [451 Mar. 4, 1975 APPARATUS FOR DETERMINING THE TENSILE STRESS IN A CONTINUOUSLY MOVING WEB OF MATERIAL [75] Inventor: Eberhard Breyer, Herrenberg,

Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany [22] Filed: Nov. 16, 1973 [2]] Appl. No.: 416,348

[30] Foreign Application Priority Data Primary Emmincr-Charles A. Ruehl Attorney, Agent, or FirmKenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT An apparatus for measuring the tensile stress of a continuously moving gas and liquid impermeable web of material, including a pair of spaced apart rollers disposed below the web for deflecting the web of material; an elongated enclosed channel disposed between the rollers below the web having an axial length which is at least as great as the width of the web and an opening disposed therebeneath; a plurality of orifices disposed in the channel coupled to means for supplying a gas under constant pressure thereto for forming a static pressure cushion between the web and the channel; and measuring means disposed in the channel for measuring the pressure therein. The improvement of the invention comprises a plurality of triangular shaped chambers which are axially disposed in series in the channel. Each of the chambers includes a partition member disposed parallel to the direction of movement of the web which forms at least one wall of each of the triangular shaped chambers. Selected ones of the chambers disposed at the outermost axial ends of the channel are provided with additional orifices communicative with the channel and coupled to means for controlling the supply of gas thereto from the channel, for compensating for gas losses at the latcral edges of the web.

6 Claims, 4 Drawing Figures r LIENTEU W 41375 sum 1 or 2- MANOMETERI APPARATUS FOR DETERMINING THE TENSILE STRESS IN A CONTINUOUSLY MOVING WEB OF MATERIAL BACKGROUND OF THE INVENTION 1. Field Of The Invention The invention relates generally to stress measurement devices, and in particular to an apparatus for determining the tensile stress of a continuously moving gas and liquid impermeable web of material by means of pressure measurement.

2. Description Of The Prior Art Tensile stress measuring devices are known in the prior art, and generally comprise an elongated channel which has an axial length which is at least as great as the width of the continuously moving web of material beneath which it is disposed. This channel has an opening which is subdivided by partition members into a plurality of serial chambers each of which open towards the underside of the web of material. A pressure measurement device, such as a manometer, is coupled to the chambers to measure the pressure produced therein by a gas supplied to the channel at a constant pressure. A plurality of orifices disposed in each chamber eject the gas towards the bottom side of the web so as to cause a gap to be formed between the moving web of material and the channel chambers. Since the volume of gas fed to the chambers is equal to the volume of gas flowing from the chambers through the described gap, a static pressure cushion supporting the web is formed.

It has been found to be advantageous to design the channel chambers so that the axial length of each chamber is small compared to the distance separating the rollers which deflect the web of material. When such relative dimensions are maintained the volume of gas which flows from the gap at the lateral edges of the web is negligible compared to the volume of gas which flows from the gap along the axial edges of the channel both in and against the direction of travel of the web. This is particularly true for wide webs of material.

Webs of material which are subject to greater tensile stresses during processing thereof, such as, for example. strip material used in cold rolling mills, require a gap between the web and the channel which is sufficiently large to form a high pressure static cushion therebeneath. Thus, the axial length of the chambers must be greater than that necessary to produce a sufficient static pressure cushion for webs of paper or foil material. As a result, cold rolling mill devices can require that the ratio of the width of the web of material with respect to the axial length of the channel chambers be approximately :15 Gas losses at the lateral edges of the web must therefore be compensated for in such cases so that when the web is in a perfectly plane condition a uniform static pressure distribution in the gas cushion is produced for the channel chambers covered by the web of material.

Effecting such compensation, however, presents considerable practical difficulty since it is necessary to accurately monitor the volume of gas required to compensate for the lateral channel edge gas losses. Since the above described heretofore known measurement devices are practicable for determining the tensile stress of webs of material, but can only be used to control the flatness of cold rolled strips of material if the distribution of the gas over the channel chambers does not produce measuring errors with respect thereto, it is desireable to provide a more accurate measuring device for monitoring the volume of gas supplied under pressure to the channel chambers to compensate for the described lateral edge losses.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an apparatus for measuring the tensile stress of a continuously moving gas and liquid impermeable web of material which overcomes the aforementioned disadvantages of prior art measurement devices.

This and other objects are achieved by the invention in an apparatus for measuring the tensile stress of a continuously moving gas and liquid impermeable web of material, which includes a pair of rollers disposed therebeneath for deflecting the web of material, an elongated enclosed channel disposed between the rollers below the web having an axial length at least as great as the width of the web and an opening disposed therebeneath. A plurality of first orifices disposed in the channel opening are coupled to means for supplying a gas to the channel under constant pressure and forming a static pressue cushion between the web and the channel opening. Means for measuring the static pressure cushion in the channel opening is also disposed therein. The improvement of the invention comprises a plurality of triangular shaped chambers axially disposed in series in the channel opening which each include a partition member disposed parallel to the direction of movement of the web transverse to the channel axis which forms at least one wall of each of the channel chambers. Selected ones of the chambers disposed at the axial ends of the channel include a plurality of additional orifices, communicative with the channel and spaced apart from the first orifices, which are coupled to means for selectively controlling the supply of gas to said additional orifices from said chamber.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top, plan, schematic view of one embodiment of an apparatus for measuring the tensile stress of a continuously moving web of material constructed according to the invention;

FIG. 2 is a partial, cross-sectional view of the measuring apparatus illustrated in FIG. 1;

FIG. 3 is a partial, top, plan, schematic view of another embodiment of a measuring apparatus constructed according to the invention;

FIG. 4 is a partial, top, plan, schematic view of the measuring apparatus illustrated in FIG. 3, showing the apparatus displaced axially with respect to the web of material.

DETAILED DESCRIPTION Referring now to the drawings, in particular FIGS. 1 and 2, there is shown one embodiment of a measuring apparatus constructed according to the invention comprising a pair of spaced apart rollers 2 and 3 separated by a predetermined distance A and disposed below a The length of the channel in the axial direction is at least as great as the width of the web of material 1. Chambers 5 each include a partition member 6 which is disposed transverse to the axis of the channel and parallel to the direction of movement of the web. Diagonal partition members 6a are disposed between adjacent partition members 6 to form the triangular shaped chambers 5. As illustrated in FIG. 1, adjacent partition members 6 form adjacent chambers 5 therebetween.

A plurality of calibrated, tapered orifices 8 are disposed in the bottom portion of each of chambers 5 of the channel and admit gas from channel 4 to the underside of web 1. These orifices are disposed at opposing ends of adjacent chamber pairs. Means, illustrated as blower 9, coupled to channel 4, supplies a gas under constant pressure thereto and orifices 8 so as to produce a static pressure cushion between channel 4 and the web of material. The blower distributes the gas throughout channel 4 so that the same constant pressure exists at the orifices in each of chambers 5. The pressure cushion is produced by the gas between the web of material and those chambers of the channel which are completely covered by the web of material, and lifts the web of material above the channel to form a gap 10 therebetween. The cushion pressure moves the web against a normal force produced by the tension forces acting thereon so that the volume of gas flowing into chambers 5 through orifices 8 is equal to the volume of gas flowing out of gap la between the web and the channel.

It has been found that the static pressure of the described gas cushion is a function of the tensile stress prevailing in the web of material which extends over at least the width thereof, and that the distribution of the static pressure over the width of the web is a conformal image of the tensile stress. Continuity conditions for the gas flowing from gap 1a dictate that the ratio of the volume of gas which must be supplied to compensate for lateral web edge losses at the axially outermost chamber 5 covered by web 1 with respect to the volume of gas supplied to each individual chamber must be equal to the ratio of the length of the side of each chamber 5 which is parallel to the direction of movement of the web, i.e., the length of members 6, and the side of each chamber disposed perpendicular thereto namely, the ratio b/a. Means for measuring the static pressure cushion, such as, for example, a manometer, in the channel opening is coupled to a remote pressure sensing means, illustrated as measuring tubes 10 and coupling lines 11, disposed in chambers 5. The tensile stress in the web of material can be determined from an accurate representation of the stress distribution by the static pressure in the gas cushion when the ratio of the width B of the web of material with respect to the length b in the axial direction of each chamber (B/b) is greater than or equal to 30 since the lateral edge gas loss is negligible. When the ratio B/b is, however, substantially less than 30, the described lateral edge gas loss must be compensated for by additional gas supplied to the chambers of the channel which are the axially outermost covered by the web.

Accordingly, selected ones of chambers 5 of the channel at the outermost ends thereof are provided with additional orifices 12 which are communicative with channel 4 and spaced apart from orifices 8. Means, illustrated as housing 13 having an opening 14 disposed below orifices 12, and a displaceable valve means shown as a valve disc 15, axially moveable by means of a pneumatic pressure cylinder 16, is coupled to each of the selected chambers to control the flow of gas from channel 4 into housing 13 and through orifices 12. Whenever compensation is required at the lateral edges of the moving web, valve 15 is opened to admit gas to the underside of the web of material through orifices 12. As noted previously, adjacent partition members 6 form adjacent pairs of chambers 5. As shown in FIG. 1, the selected chambers 5' comprise only one chamber of any such adjacent pair. Measuring tube 10 is disposed in the other chamber of any such pair including a selected chamber 5 so that the static pressure measurement is not affected by the additional gas admitted by orifices 12 to the underside of web 1. Since the determination of tensile stress in a web of material may be required over a wide range of widths, it is preferable to provide several chambers 5 at the outer axial ends of the channel.

FIGS. 3 and 4 illustrate another embodiment of the apparatus illustrated in FIG. 1 in which the selected chambers are spaced apart by a distance which is at least equal to the width a of the chambers. In FIG. 3, web 1 has a width B which covers selected chambers 17 and 17'. Accordingly, the valve disks 15 of the housings which are coupled to these chambers are opened to admit gas through orifices 12 to the underside of web 1. FIG. 3 also illustrates the minimum and maximum web widths max. B and min. B which can be utilized. If the width of the web of material is to be varied by, for example, two to four chamber widths (a), channel 4 is shifted axially transverse to the direction of travel of the web of material. A strip of width B 2a, for example, then covers chamber 18 at one end of the channel and chamber 17 at the other end thereof. The valves for chambers 17 and 18 are then opened to permit gas to flow through orifices 12. Because such a web has a greater width, it spans a greater number of chambers, and consequently, 6 instead of 5 measuring tubes are available to measure the gas pressure below the web of material.

The apparatus of the invention provides numerous advantages over prior art devices. In particular, the flow resistance of the valve means disposed below orifices 12 is negligible compared to the pressure of the gas supplied to the channel by blower 9. Consequently, the dimensions and number of orifices 12 required can be determined in an extremely accurate manner as a function of the ratio of the length of the sides of the chambers. Simple manufacturing methods can thus be utilized to implement the provision of these additional orifices. This precludes the necessity and expense of readjusting the orifices in accordance with sample measurements of the pressure and gas flow rate.

While there have been disclosed herein what are considered at present to be the preferred embodiments of the invention, it will be apparent to those persons skilled in the art that many changes and modifications may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawing are accordingly to be regarded in an illustrative rather than in a restrictive sense.

What is claimed is:

1. An apparatus for measuring the tensile stress of a continuously moving gas and liquid impermeable web of material, including a pair of rollers disposed therebeneath for deflecting the web of material, an elongated enclosed channel disposed between the rollers below the web having an axial length at least as great as the width of the web and an opening disposed therebeneath, a plurality of first orifices disposed in the channel opening, means coupled to the channel for supply ing a gas thereto and to said orifices under contant pressure and thereby forming a static pressure cushion between the web and the channel opening, and means disposed in the channel opening for measuring the pressure of the cushion, the improvement comprising:

a plurality of triangular shaped chambers, axially disposed in series in said channel opening, and each including a partition member disposed parallel to the direction of movement of the web which forms at least one wall of each of said chambers, selected ones of said chambers at the axial ends of said channel including a plurality of additional orifices communicative with said channel and spaced apart from said first orifices; and means, coupled to said selected chambers, for selectively controlling the supply of said gas to said additional orifices from said channel. 2. The apparatus recited in claim 1, wherein said means for controlling the supply of gas to said additional orifices comprises a housing disposed below said additional orifices of each of said selected chambers and coupled thereto, including an opening communicative with said additional orifices, and displaceable valve means, disposed adjacent said housing opening for con trolling the admittance of said gas to said housing and said additional orifices from said channel.

3. The apparatus recited in claim 2, wherein said chambers are approximately equal in width, and wherein said selected chambers at: the same axial end of said channel are separated by a distance equal to at least the width of said chambers.

4. The apparatus recited in claim 2, wherein adjacent partition members form therebetween adjacent pairs of said chambers, said selected ones of said chambers comprising only one chamber of any such adjacent pair.

5. The apparatus recited in claim 4, wherein said pressure measuring means includes remote pressure sensing means, said sensing means being disposed in the other of said chambers of any adjacent pair including said one selected chamber.

6. The apparatus recited in claim 4, wherein said first orifices are disposed at opposing ends of said chambers forming said adjacent pairs and said additional orifices are disposed in said selected chambers between said first orifices. 

1. An apparatus for measuring the tensile stress of a continuously moving gas and liquid impermeable web of material, including a pair of rollers disposed therebeneath for deflecting the web of material, an elongated enclosed channel disposed between the rollers below the web having an axial length at least as great as the width of the web and an opening disposed therebeneath, a plurality of first orifices disposed in the channel opening, means coupled to the channel for supplying a gas thereto and to said orifices under contant pressure and thereby forming a static pressure cushion between the web and the channel opening, and means disposed in the channel opening for measurIng the pressure of the cushion, the improvement comprising: a plurality of triangular shaped chambers, axially disposed in series in said channel opening, and each including a partition member disposed parallel to the direction of movement of the web which forms at least one wall of each of said chambers, selected ones of said chambers at the axial ends of said channel including a plurality of additional orifices communicative with said channel and spaced apart from said first orifices; and means, coupled to said selected chambers, for selectively controlling the supply of said gas to said additional orifices from said channel.
 2. The apparatus recited in claim 1, wherein said means for controlling the supply of gas to said additional orifices comprises a housing disposed below said additional orifices of each of said selected chambers and coupled thereto, including an opening communicative with said additional orifices, and displaceable valve means, disposed adjacent said housing opening for controlling the admittance of said gas to said housing and said additional orifices from said channel.
 3. The apparatus recited in claim 2, wherein said chambers are approximately equal in width, and wherein said selected chambers at the same axial end of said channel are separated by a distance equal to at least the width of said chambers.
 4. The apparatus recited in claim 2, wherein adjacent partition members form therebetween adjacent pairs of said chambers, said selected ones of said chambers comprising only one chamber of any such adjacent pair.
 5. The apparatus recited in claim 4, wherein said pressure measuring means includes remote pressure sensing means, said sensing means being disposed in the other of said chambers of any adjacent pair including said one selected chamber.
 6. The apparatus recited in claim 4, wherein said first orifices are disposed at opposing ends of said chambers forming said adjacent pairs and said additional orifices are disposed in said selected chambers between said first orifices. 